What do we know about individuals who reach near-native levels of proficiency in a foreign language? Multiple paths!
Achieving Native-Like Second Language Proficiency (Speaking) by Betty Lou Leaver is a research-based catalogue of factors that would seem to predict ability to reach the highest level of foreign language proficiency and is based on common characteristics shared by more than 200 near-native speakers, identified by self-report, survey, and interviews by master testers. This study showed that there are multiple paths to native-like foreign language proficiency -- and subsequent studies have confirmed this. Even the same person who is trilingual or quadrilingual takes a different path to acquiring each of those languages. Age of language learning onset, location(s) of language learning, prior language learning experience, influence of teachers and educational approaches, and opportunities (or lack of them) for cross-cultural experience, including when in a professional career those opportunities appear all shape the path followed by an individual for acquisition of a particular language